Planet Candidate 'Xena' Has a Moon

Xena, the possible 10th planet in our solar system, has its own moon, a dim little satellite called Gabrielle, its discoverers reported.

Astronomers who reported Xena's discovery in July said they detected Gabrielle on Sept. 10 using the Keck Observatory on Mauna Kea in Hawaii. Their findings are to be submitted to the Astrophysical Journal Letters today.

Xena, known formally as 2003 UB313 but nicknamed for the warrior princess of television fame, and Gabrielle orbit the sun out beyond Pluto in a band known as the Kuiper Belt, a swath that is home to comets, asteroids and other space rocks.

The International Astronomical Union, which makes the decision on what is a planet, considers Xena a trans-Neptunian object, meaning its orbit crosses that of Neptune, just as Pluto's does. Many astronomers question Pluto's planetary status, too. But Xena's discovery, and its size, have prompted the union to rethink the definition of a planet.